Obstacle detecting devices for a vehicle have been invented, some of which estimate a receiving time of a reflected wave accurately, even when amplitude of the received reflected wave is fluctuant. For example, one of such obstacle detection devices is disclosed in the Japanese Patent Publication JP2005-69867A.
The obstacle detection device disclosed in JP2005-69867A estimates an envelope (an envelope wave) of reflected wave, which are full-wave rectified, and then estimates an approximate straight line by approximating a starting point of the envelope wave using two points where the envelope wave intersects with two threshold values of the different voltage values. Then, the device estimates a time when the approximate straight line and 0 voltage (0V) of the voltage value are crossed (zero-cross time). In this configuration, even when the amplitudes of the reflected waves are fluctuated, and consequently inclination of the approximate straight line is changed, the point (value) of the zero-cross time is not fluctuated. Therefore, by the use of the zero-cross time, a receiving time of the reflected wave is accurately estimated, and eventually a location of the obstacle (a location and a direction) is precisely determined.
The obstacle detection device disclosed in JP2005-69867A estimates the approximate straight line that approximates the upstroke of the envelope wave. However, when a rise occurs on the upstroke of the envelope wave, this known obstacle detecting has difficulties in estimating the appropriate approximate straight line. As a consequence, the accurate zero-cross time is not calculated. For example, as shown in FIG. 11, when a rising occurs on the upstroke of the envelope wave, an approximate straight line L11 or an approximate straight line L12, which correspond to each rise, are calculated, and thus resulting in a failure to recognize an approximate straight line L13 as a primary approximate straight line. Therefore, the zero-cross time T3 of the approximate straight line L13 differs from the zero-cross time T1 of the approximate straight lines L11 and/or the zero-cross time T2 of the approximate straight line L12. As a consequence, a level of accuracy in determining a distance and a direction of the obstacle eventually decreases.
A need thus exists to provide an obstacle detection device and a method for estimating the receiving time that calculate the receiving time of each of the reflected waves accurately by appropriately determining a peak of the envelope wave, and consequently detect a location of an obstacle with accuracy.